1. Field of the Invention
The present invention relates generally to a power amplifier, and more particularly to a power amplifier capable of demodulating a PCM (pulse code modulated) signal and simultaneously producing power amplification.
2. Description of the Prior Art
Recently, in the audio art a digital technique has begun to be employed. According to such technique, and audio signal is converted into a PCM signal and then recorded and later reproduced. However, the transmission of a digital signal requires a wide transmission band as compared with the transmission of an analog signal and it is necessary to detect errors produced in the transmission system and to correct the errors, so that the digital signal transmission is effected in only a narrow area.
At present, the PCM technique in the audio art is employed mainly in the recording part of the whole signal transmission system from a microphone to a speaker but is not employed in an audio system comprising only an amplifier and a speaker. The digital signal which is recorded in a PCM recorder is demodulated back into an analog signal, and this analog signal is then amplified by an analog amplifier and fed to the speaker. Thus, the frequency characteristic of the amplifier and its distortion characteristic become a problem, and much power is consumed, which results in very low efficiency.